Catalytic (thermal) polymerization of tall oil fatty acids produces a product known as dimer/trimer acid which the oil industry has traditionally employed as an oil-soluble corrosion inhibitor for reducing corrosion in oil well piping and related recovery equipment. The thermal polymerization causes the C18 tall oil fatty acids (containing one or two double bonds, e.g. oleic and linoleic acids, respectively), in the presence of a suitable catalyst, to give varying amounts of C36 (dimerized) and C54 (trimerized) fatty acids. These dimer and/or trimer fatty acids may be neutralized with an appropriate amine, such as diethylenetriamine, to produce a corrosion inhibitor. The dimer/trimer acid-based product is said to inhibit corrosion by coating metal surfaces with a thin film, thereby excluding the water necessary for corrosion processes to occur.
Over the years, the corrosion inhibition art has looked for alternatives to the dimer/trimer acid-based product. Of particular interest in this regard is the class of fatty acid-based products which have been functionalized with maleic anhydride and/or fumaric acid.
Thus, according to U.S. Pat. No. 4,927,669, tall oil fatty acid (TOFA) is functionalized using maleic anhydride, or fumaric acid, in the presence of a catalyst such as iodine, clay or silica. The fatty acids are reacted in a first step to promote a Diels-Alder reaction with linoleic acid, the product then being distilled to remove unreacted fatty acid. In a second step, non-conjugated acid, e.g., oleic/elaidic acids, are treated under more vigorous conditions to form an ene adduct. Residual unreacted fatty acid is removed. The product is said to contain 75 to 95% maleinized fatty acids, 15 to 20% thermal dimer and trimer and unreacted fatty acid and is useful as a corrosion inhibitor.
U.S. Pat. No. 5,292,480 condenses the maleic anhydride-functionalized TOFA of U.S. Pat. No. 4,927,669 with a polyalcohol, such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, pentaerythritol, trimethylolpentane, and sorbitol to form an acid-anhydride ester corrosion inhibitor, which in turn may be neutralized with an amine, with a metal oxide, or with a hydroxide before use. U.S. Pat. No. 5,385,616 is similar in describing the reaction product of the maleic anhydride-functionalized TOFA of U.S. Pat. No. 4,927,669 and an alcohol (ROH).
In U.S. Pat. No. 5,582,792, the maleic anhydride-functionalized TOFA is esterified (as in U.S. Pat. No. 5,385,616 and then is reacted with an ethoxylated amine, such as an ethoxylated fatty amine. The composition is useful for corrosion inhibition.
U.S. Pat. No. 5,759,485 describes a class of water soluble corrosion inhibitors in which the maleic anhydride-functionalized TOFA (specifically the Diels-Alder reaction adduct with linoleic acid) is neutralized with aminoethylethanolamine and also with one of imidazoline, amidoamine or a combination thereof. Canadian Pat. 2,299,857 describes a similar corrosion inhibitor made by reacting (neutralizing) maleated TOFA with alkanolamines.
As evidenced by the foregoing prior art attempts to develop corrosion inhibitors based on maleated TOFA, those skilled in the art continue to explore new techniques and compositions for using tall oil-related raw materials in manufacturing new corrosion inhibitors and other products.